"Ricardo Sa Pinto no longer coaches the team," the club told the Portuguese stock market.
His dismissal came two days before Sporting, who are seventh in the league with six points from five games, travel to arch-rivals Porto for the "Classico".
One of Portugal's 'Big Three', along with Porto and Benfica, Sporting have disappointed in recent years.
The Lisbon team have failed to win the title since 2002 and finished 16, 28 and 36 points behind the champions in the last three seasons.
Sporting last qualified for the Champions League four years ago and are bottom of Europa League Group G with one point from two matches.
They lost at Videoton on Thursday.